1. Field of the Invention
The present invention relates to a method and a device for distributing a predetermined number of sheets from a group of sheets, the group of sheets comprising a plurality of sheets which are arranged in a shingled mode of arrangement in a sheet or paper transport direction in such a way that the leading edges of the sheets in the paper transport direction are spaced apart in the group by a certain length of displacement.
2. Description of Related Art
In the prior art, paper handling systems are known in which e.g. 2-up printed sheets are supplied to a cutter, separated from one another by this cutter and then placed ready for further processing by a subsequent device. For this purpose, the 2-up printed sheets are placed one on top of the other by means of suitable machines, such as mergers, and, in this condition, they are applied to subsequent paper handling machines for further processing.
For further processing the individual sheets provided in this way, the subsequent machines take over, per machine clock cycle, one such waiting sheet; depending on the subsequent machines, individual groups must e.g. be formed from the sheets provided, these groups being then e.g. put in envelopes.
The clock cycle with which the cutter operates and with which the individual sheets are made available to the subsequent machines is faster than the clock cycle of a subsequent enveloping unit. By way of example, it is assumed that the cutter can carry out 1,000 cutting operations within a predetermined period of time, whereas the enveloping unit can carry out 100 enveloping operations within this period of time. This has the effect that, in a first case, in which the enveloping unit processes only single sheets, the cutter will be stopped at certain intervals, since it would provide too many sheets, whereas in a second case, in which the enveloping unit envelops fifteen sheets at a time, the enveloping unit will have to be stopped at certain intervals, since the cutter is not able to provide a sufficient number of sheets. The prior art already discloses solutions which, for avoiding the disadvantages resulting from the above, interpose a buffer between the cutter and the subsequent machines so as to permit a continuous operation of the cutter. In this case, the individual sheets discharged by the cutter are introduced in the buffer, and, when a predetermined number of sheets has been reached, switching over to e.g. a second buffer plane is effected so that the sheets contained in the first buffer plane can be advanced for further processing, whereas sheets discharged by the cutter are simultaneously introduced in the second buffer. Such a device is described e.g. in U.S. Pat. No. 5,083,769.
Devices of this type are, however, disadvantageous insofar as the transfer of the sheets which are discharged by the cutters and which have been merged by the merger takes too much time, since the individual sheets must be transferred to the buffer one after the other. When the sheets are provided in pairs, two sheets at a time can be transferred in parallel. In the case of large groups two sheets at a time are transferred in parallel, the respective pairs of sheets being transferred in succession. Furthermore, the performance will be impaired in the case of comparatively large buffers or uneven numbers of sheets or group sizes or in the case of even numbers of sheets and a discharge which does not take place in pairs, since, for forming a group, such systems need two or more clock cycles depending on the number of sheets.
DE 197 43 020 A1 describes a device for singulating printed products provided in the form of a succession of printed products overlapping one another in a shingle-like manner. The leading printed product in the “shingled stream” is seized and advanced at a higher speed in the singulating device so that a distance to the following printed products is established, whereby the desired singulating effect is produced. Instead of complete singulating, it is also possible to change the degree of overlapping of the shingled stream by means of suitable control. Formation of a group comprising a plurality of sheets is not possible.
German-Offenlegungsschrift 2 207 175 shows a device for forming stacks. A first conveying belt has individual sheets supplied thereto in a clocked mode; depending on the clock, these sheets are deposited in a shingled mode of arrangement on the first section of the conveying belt. A removing mechanism is moved via a carriage and an oscillating movement of the carriage is provided so that, during the whole advance movement of the carriage, not a single copy will be removed and deposited on a further conveying belt moving at a higher speed and so that, during the return movement of the carriage, copies seized by a roll are supplied to the collecting magazine at a higher speed. This has the effect that a gap is formed in the continued transport on the conveying belt.